1. Field of the Invention
This invention relates to an endless metal belt, and a coated belt obtained by coating the metal belt, which are used for image forming apparatuses, such as copying machines, facsimiles, and laser beam printers.
2. Description of the Related Art
To meet demands such as miniaturization, reduction in the power consumption, and increase in the speed of printing and copying of image forming apparatuses, there has been adopted a belt fixing method, in which an endless fixing belt (endless belt or tube) is driven to be rotated instead of a fixing roller. A fixing belt has the advantage that waiting time after turning on the power is reduced, since a toner image on a transfer member can be almost directly heated and fixed, with only a thin belt intervening, by bringing heating means into contact with an internal surface of the fixing belt.
In such a fixing belt, a release layer is formed by coating directly, or with an elastic layer intervening, on an endless metal belt base material. In most cases, a release layer is made of a heat-resistant resin having excellent heat-resistance and releasing property, such as fluoroplastics. Since a release layer made of heat-resistant resin lacks elasticity, in most cases an elastic layer is disposed between the metal belt base material and the release layer, to improve fixing property and image quality. If the release layer is a rubber layer having elasticity and releasing property, such as a silicone rubber layer, an intermediate elastic layer can be omitted. As a transfer belt, a charged belt, and a conveyer belt, used is an endless belt made of a metal belt base material alone, or of a metal belt base material and a release layer.
U.S. Pat. No. 6,564,033, Jpn. Pat. Appln. KOKAI Pub. No. 2002-241984 and Jpn. Pat. Appln. KOKAI Pub. No. 2002-148975 disclose an endless nickel belt formed as a metal belt base material by using electroforming.
U.S. Pat. No. 6,564,033 discloses an electroformed nickel belt, in which a plane (200) is preferentially grown, in which the electroformed nickel has a crystal orientation ratio I(200)/I(111) of 3 or more, preferably 8 or more, and a carbon content of electroformed nickel is not more than 0.08 wt %.
Jpn. Pat. Appln. KOKAI Pub. No. 2002-241984 discloses an electroformed nickel belt containing at least one additive element selected from the group consisting of thallium, lead, bismuth, tin, calcium, zinc, aluminum, silicon, and antimony.
Jpn. Pat. Appln. KOKAI Pub. No. 2002-148975 discloses an electroformed nickel belt whose carbon content is 0.01 to 0.1 wt %.
However, conventional nickel belts do not have sufficient fatigue strength at high temperature, and lack durability. In the belt fixing method, a belt is repeatedly bent in a fixing nip part and an inlet and outlet thereof with rotation of the belt itself, and torsion is caused on the belt by difference in the peripheral speed. Therefore, the belt tends to be mechanically fatigued, and has a problem in heat resistance and durability. For example, its endurance time is shortened by increasing the fixing temperature. In particular, since the fixing nip part of a high-speed printer is wide and has a high pressing force, mechanical force applied on the belt increases, and a high fixing temperature is set. Therefore, the conventional belts tend to be broken for a relatively short time, and must be replaced with high frequency.
Further, in a belt having a high carbon content, a plating film has an increased internal stress. Therefore, its releasing property decreases, an electroformed product is not easily removed from a matrix, and a part of the electroformed product may be separated from the matrix during electrolysis due to excessive internal stress.